The present invention relates generally to a system for settling fine particles from a contaminated fluid, and more particularly to a filter system that utilizes a cartridge that, due to construction and orientation, effects separation of relatively fine particles from a liquid by gravity settlement of the particles.
Fine particles produced in certain industrial operations are difficult to remove from a host fluid, such as a coolant utilized in cooling systems to prevent damage to machining equipment due to excessive temperatures. Typically, a water soluble oil coolant is commonly used in known cooling systems. Soluble oil is an emulsion wherein water is the continuous phase and oil is the disperse phase. The soluble oil emulsion comprises globules composed of emulsifying agents and oil, wherein the globules are approximately 0.1 to 0.3 microns in size. The emulsifying agents, or emulsifiers, hold the oil in a stable suspension in the water by preventing the oil globules from increasing in size.
Soluble oil coolants are corrupted over time by solid particulates that are suspended in the coolant. For example, during machining of aluminum, a very thin oxide typically develops on the surface of the aluminum under ambient conditions. When aluminum parts are machined, rolled, or punched, the aluminum oxide, or alumina, tends to peel off the surface and become entrained in the machining coolant. Aluminum oxide particles are extremely abrasive and create a grit filled coolant that is destructive to the machining equipment. In addition to creating a grit filled coolant, the aluminum oxide particles also interfere with emulsifying soaps present in soluble oils. These soaps are usually in the form of sodium salts of fatty acids. When aluminum oxide particles become entrained in the soluble oil, an undesirable ion exchange is established wherein aluminum from the aluminum oxide displaces the sodium in the soluble soap, thereby rendering the soap insoluble. Insoluble soaps are problematic because they plug, or "foul," the filtration media.
The presence of fine particles in a host fluid is not limited to large systems. For example, in conventional engine oil lubrication systems, abrasive particles contaminate the petroleum-derived mineral oil and similarly create wear and tear on the engine.
Conventional cartridge or media type filters are generally utilized to remove suspended solids from a host fluid. However, permanent media filters often require backwashing in order to remove entrapped particles that plug the filter. In the area of cooling systems for industrial machining processes or systems, such backwashing disposes particles, such as alumina, immediately back into the cooling system. Large particles, e.g., greater than 30-250 microns in size, then settle in the cooling system and may be removed by conveyors. However, smaller particles do not settle and are simply not removed, thus further accumulating in the cooling system. The smaller particles are eventually milled into even smaller, often colloidal, particles. As the concentration of these impurities increases over time, the coolant must be replaced by a fresh emulsion, thereby reducing production time by shutting down the machining process. In addition, disposal of spent coolant creates ecological and environmental concerns.
Conventional cartridge filters have a restricted surface area and thus a limited capacity for holding separated solid matter and/or insoluble soaps. Conventional cartridges must therefore be continually discarded and replaced with a new cartridge. For example, conventional pleated automotive engine oil cartridge filters are frequently plugged and inoperative because of limited dirt holding capacity.
Filtration of colloidal or submicronic particles has heretofore been particularly difficult. For example, colloidal alumina particles suspended in a coolant emulsion used in cooling systems for industrial operations are generally smaller than one micron. However, any attempt to specifically filter out the colloidal alumina particles tends to destroy or break down the stability of the globules, which in turn breaks down the stability of the coolant.
In addition, filtration of fine particles has been found to be further problematic because of the very fine porosity required by fine particle filters. For example, filter aids, in a form of a precoat material such as diatomaceous earth, have heretofore been used to maintain the porosity of a filter cake used in fine particle filters so as to minimize blinding and channeling of the host fluid. However, environmental concerns have placed severe restraints on industrial use of such filter aids because of the hazard they create when they are introduced to the host liquid. In many cases such filter aids are carcinogens.
One solution to this problem is to use paper filters of extremely fine porosity. However, when extremely fine particles are filtered through two-dimensional paper of a porosity fine enough to capture the particles, the flow rate very shortly diminishes and the filter paper tends to blind off, thereby attenuating flow of fluid through the filter. Thus, a great deal of filter paper has to be used which is extremely expensive and difficult to handle. Therefore, a need exists for a filter system that effectively removes extremely fine particles from a contaminated fluid in a manner that minimizes both environmental hazards and the cost and efficiency of filtration.